Former Sen. Rick Santorum (R-Pa.) on Wednesday backed former Rep. Pete Hoekstra in his bid against Sen. Debbie Stabenow (D).

Santorum’s endorsement comes a few days before Michigan’s Republican Senate primary, which is set for Tuesday. Hoekstra’s main competition in that race is charter schools executive Clark Durant. Republicans expect Hoekstra to win the nomination, but Durant has garnered endorsements from several nationally recognized conservatives, including Sen. Tom Coburn (R-Okla.).

“It is clear that the people of Michigan have tremendous choices in the Republican primary that [would all] be superior to Debbie Stabenow, but there is only one candidate with a proven track record of conservative leadership,” Santorum said. “That is Congressman Pete Hoekstra.”

The winner of the GOP primary has a tough battle ahead. Roll Call rates this Senate race as Likely Democratic.